Course pitch spur gear tolerance query 2

[morris9791]

Dear Experts,

I am currently looking at the AGMA standard as regards runout, pitch, profile and lead tolerances for spur gears.

Is it normal practice/acceptable to linear interpolate these values for different module and pitch diameters that are not tabulated in AGMA standard?

Any information will be appreciated.

Best Regards
Eddie

 

[morris9791]

Experts,

Furthermore, is there really a need to provide this tolerance data on the engineering drawing? Is the AGMA number just sufficient along with gear geometry data?

Thanks
Eddie

 

[israelkk]

It is sufficient as long as you specify the AGMA version (such as 390.02, 390.03, 2000-A88 or the newest 2015).

Note that AGMA tolerance values are just tolerances. You need to specify the value that those tolerances are refers too. This is usually done with a Minimum and Maximum testing radius on a double flank testing machine when the gear is mesh against a master gear.

 

[morris9791]

Dear Israelkk,

It appears I need to specify the runout, pitch and profile tolerances since I am dealing with truncated 'gear' teeth that have to couple/match with 'splined' teeth.

How does one determine these tolerances for a given normal diametral pitch of 25.4/2.75 = 9.23 and a pitch diameter of 70*3/25.4 = 7.58.

The attached pdf illustrates values for diametral pitch of 4 and 8 and pitch diameter of 6 and 12. I am not sure if these values can be correctly interpolated since we are dealing with 2 variables i.e., the pitch diameter and diametral pitch...

Please bear with me as I am quite new to gear design.

Best Regards
Eddie

 

[israelkk]

What are you trying to do? Are you trying to use the spline as a driving pinion? Splines pressure angle is normally different then pressure angle of gears.

 

[morris9791]

Israelkk,

I am looking at a particular application of a ring gear and its carrier. They are coupled together and there is no relative movement between them.

On the ring gear carrier, a specially formed splined is machined to match the truncated teeth profile on the ring gear.

So yes, the spline will have a pressure angle of 20 instead of 30 to match the ring gear. We use ANSI 92.2M “Metric Module Involute Splines” to obtain the special spline data.
The approach is used successfully in all our applications.

I am just in the process of learning how to obtain these particular tolerances which was the aim of this query.

Any information will be appreciated.
Best Regards
Eddie

 

[tbuelna]

morris9791,

The AGMA tolerances for things like PL runout, composite and tooth-to-tooth index errors, profile, lead, etc. are recommendations. And yes, the published values should be interpolated for non-standard DP's or modules.

But as with most design standards, these values are just guidelines. And if you are doing something that deviates from these guidelines, you will need to make adjustments.

As for specifying things like lead correction/crown, profile modifications, index tolerances, pitch line runout, etc., it is absolutely necessary. If you don't specify these details, then how do you expect your gear vendor to produce a gear that meets your requirements? With high performance gears, these types of small details can make huge differences in the performance and life of your gears.

You state that you have a ring gear and planetary carrier that are coupled by an external involute spline on the carrier that is designed to match the internal gear teeth of the ring gear. Involute spline and gear teeth have similar geometries, but only if their parameters (such as pressure angle) agree. If the pressure angles are different, then the tooth profiles will not match above and below the pitch line. And this will lead to either edge loading at the roots/tips, or inadequate space width in the internal spline to permit engagement of the external spline.

You also indicate that there should be no "relative movement". Most involute spline joints have some tangential clearance in order to allow them to be easily assembled. But in order to ensure that all of the spline teeth share the torque load equally, the tooth width, space, and index errors must be controlled. And if the spline has a long axial engagement, lead corrections must also be considered to prevent edge loading.

Finally, the type of spline fit you require is also important. To mate with a gear, you likely want a fillet root, side fit spline. Make sure to specify adequate tooth tip breaks so that the tooth tip edges don't bear into the root fillets.

Hope that helps.
Terry

 

[dinjin]

They used to append the standard with the calculations and you could use those to get your results rather than interpolating.

 

[mfgenggear]

as manufacture of gears
these are the usual or some of the mistakes encountered.

root radii fillet is specified to big, results interference.
missing or wrong form diameter

gear or spline attributes not specified to a datum.

Omitted attributes if no AGMA or spline quality class specified.
lead (parallel) tolerance
tooth to tooth error or pitch variance.
Pitch diameter run-out not specified
Involute tolerance chart omitted

Measurement over/between wires does not match tooth/space.or missing or wrong wire size.

heat treat not specified correctly


As the designer. he or she is responsible to make sure
the attributes & tolerances reflect the nature
of quality vs cost for the product reliability required.

generally for Aircraft the standard spline attributes per the ANSI/ASME standards are normally satisfactory.

gears dependent on your application, precision required
AGMA standard are a good guide line. sometimes it can be
less stringent sometimes more stringent.
Extensive past experience or history & or Test will normally
result in good gear trains.
Find your self a good consultant if you have neither.
He or she will be your best friend.
Then find a good supplier/manufacture of gears, he is also is your best friend, They will be a very valuable asset if the right company is contracted.

 

[morris9791]

Thanks tbuelna, mfgenggear, dinjin

Yes the pressure angle is specified to be the same for both the gear and spline. As I have stated this has be successfully used on some of our products without any failures to the best of my knowledge. The guy who specified the coupling is no longer here so I am figuring out how is it is done since I am no gear expert.

I also came across an AGMA article which quoted that most tolerance equations in ‘Accuracy classification system -Tangential Measurement Tolerance Table for Cylindrical Gears’ are non liner and therefore linear interpolation would not be accurate!!

So I guess I need to locate this standard: AGMA 2015/915 – 1 – A02 to get access to the tolerance equations.
Does anyone know where I could source this document that may be freely available online (legally of course)?

Best Regards

 

[PeteDB]

AGMA has a tolerance calculator program available. It calculates the design tolerance to AGMA 2015-1-A01.
It is free. Look for SOFTWARE PRODUCTS on their website at

http://www.agma.org

Pete